1. Field of the Invention
This invention relates generally to the art of jet mixing and more particularly to a method and apparatus for pre-dilution of a fluid prior to discharge into a receiving body of water.
2. Prior Art
In offshore drilling it is necessary to dispose of spent or discarded drill mud and cuttings and/or produced water. Normally such spent muds and cuttings are discharged into the receiving waters. Pre-dilution may be required to prevent the discharge of a concentrated mud plume which tends to settle, since its specific gravity may be as much as two and a half times that of water. It is further theorized that when the mud settles to the bottom it forms a mound which smothers certain marine organisms. In addition, the mud or produced water is theorized to contain certain pollutants which the toxicity of is concentration dependent.
Commonly, pre-dilution if required is accomplished by pumping water into the spent mud or produced water stream from the drilling rig prior to discharge. Where only low discharge rates are allowed the existing fire water system for the rig can be modified to accomplish dilution with minimal capital investment. In cases where higher discharge rates are allowed, the fire water system may prove inadequate and a separate dedicated dilution pump and piping system may have to be installed. It is of course desirable that heavy, spent mud be discharged as rapidly as possible in order to facilitate movement of the drilling rig, since delays in these operations can be very costly.
Recent actions by regulatory agencies have placed pre-dilution requirements on the discharge of spent drill muds and cuttings into receiving waters. Certain discharge permits contain a provision requiring that the drill muds and cuttings be diluted in the ratio of at least 9:1 with the receiving water prior to discharge. A similar requirement is considered possible in the future for produced water.
The invention to be described utilizes a process known as jet mixing wherein one liquid is pumped through a small orifice into a flowing stream of another. Jet mixing is used, for example, in the chemical industry for liquid-liquid extraction. However, in the present invention jet mixing is used to dilute a fluid jet stream in a desired volume ratio with the entrained liquid rather than for dispersion of the jet stream into finely-divided droplets of any particular dimensions. The invention also utilizes the technique of aspiration, wherein the flow of one liquid (the aspirated liquid) is induced by the flow of another (the receiving liquid) at higher velocity. Contrary to common practice however, in the present invention, a larger stream is sucked into a smaller stream rather than vice versa.
It is therefore a general object of this invention to provide an improved method and apparatus for pre-dilution of a fluid such as drill mud and the like prior to free discharge into a receiving body of water.
It is a more particular object of this invention to provide a method and apparatus for pre-dilution of such fluids which is energy efficient and essentially unlimited in capacity.
It is a still further object of this invention to provide such a method and apparatus wherein discharge of a fluid stream into a receiving body of water may be constantly aligned with the current direction in said body of water.
It is yet a further object of this invention to provide a method and apparatus for pre-dilution of a fluid prior to discharge into a receiving body of water without utilizing any moving parts.
Other objects and advantages of this invention will become apparent from a consideration of the detailed description to follow, taken in conjunction with the drawings and claims appended thereto.